SE546430C2

SE546430C2 - A method of manufacturing a secondary cell

Info

Publication number: SE546430C2
Application number: SE2251078A
Authority: SE
Inventors: Chris Cook; Michael Koma
Original assignee: Northvolt Ab
Priority date: 2022-09-16
Filing date: 2022-09-16
Publication date: 2024-10-29
Also published as: WO2024056777A1; SE2251078A1

Abstract

The disclosure relates to methods of forming secondary cells, and cells formed by such methods. The cells comprise a conductive adhesive which adheres the tables electrodes to the current collector, thereby minimising the issues associated with welding these connections.

Description

The invention relates to :_ :::::;:.:*:::f:_.:i; :Lif får at. :;::\:::;{,1.' 'fc iii.. a method of manufacturing a secondary cell.

BACKGROUND In addressing climate change, there is an increasing demand for rechargeable batteries to enable greater electrification of transportation and allow for greater dependence on renewa ble energy, among other reasons. Currently, lithium-ion batteries are becoming increasingly popular. They represent a type of rechargeable battery in which lithium ions move from a negative electrode to a positive electrode during discharge, and in the opposite direction when charging.

A rechargeable battery, often referred to as a secondary battery, may comprise one or more secondary cells electrically connected to each other.

Jellyrolls, or Swiss rolls, may be used in the secondary cells. A jellyroll is a type of electrode assembly having a structure in which a positive electrode and a negative electrode, each having a long conductive sheet or foil coated with an active material, are wound with a separator interposed in-between. The wound assembly therefore has a cylindrical or "roll' shape. The roll is then placed into a casing or can. In some secondary cells, the roll is then soaked in electrolyte before the can is sealed. However, a solid electrolyte may also be used; in which case, the separator is not required.

Jellyroll secondary cells may be tab-less cells.

In tab-less cells, the conductive sheets commonly have an exposed (i.e., uncoated) part protruding from one side of the cylinder. The exposed part is connected to a terminal of the cell to allow the flow of an electrical current from the jelly roll via the terminal. To create an appropriate surface to connect a terminal to, the exposed part can be folded and/or pressed to form a surface with good contact properties while also aiming to minimize the risk of a short circuit.

Prior to connecting the terminal to the exposed part, a current collecting plate is typically welded to the exposed part. The current collecting plate protects the exposed part and provides a robust surface with further improved contact properties for subsequent connection to the terminal.

However, when welding the current collecting plate to the exposed part, direct contact or "zero gap' is required which is difficult to control. Specifically, it can be difficult to achieve a good contact between the flattened conductive sheet and the current collecting plate due to the flimsiness of the conductive sheet and the rapid speed that is required during the process. Sub-optimal contact may lead to increased resistance in the cell and premature failure.

Also, the heat required to weld the current collecting plate to the exposed part as well as particles generated during welding can damage the exposed part and/or the nearest portion of the jellyroll and cause the cell to short circuit.

SUMMARY OF THE INVENTION An object of the present invention is to manufacture secondary cells that avoid the deficiencies and risks associated with a welded current collecting plate. » " \./\». \.f\.~ * _.. \».\»*.\ .._«. . \.f \.\.«\ _' _. ..\ In some embodiments, the conductive particles comprise one or more of graphite, copper or silver particles.

In some embodiments, the electrode roll assembly comprises a second electrode wound about the central axis, the second electrode comprising an exposed part extending from a second end of the electrode roll assembly; the secondary cell comprises a second current collecting plate; and conductive adhesive joins the exposed part of the second electrode to the second current collecting plate, thereby providing electrical conductivity between the exposed part of the second electrode and the second current collecting plate.

According to a aspect of the invention, there is provided a method of manufacturing a secondary cell, the method comprising the steps of: (a) providing an electrode roll assembly fimgwand a first current collecting plate >>>> g g = l .J the electrode roll assembly i: Mcomprising a first electrode wound about a (b) bonding the first current collecting plateí 'j¿g_to the exposed part electrode with a conductive adhesive, the conductive adhesive g_.¿comprising .wdispersed therein, thereby Wof the fi rst "";:¿_a nd conductive pa rticles a polymeric binderf providing electrical conductivity between the exposed part electrode and the first current collecting plate» _.m\ . erwts. N... Am tå lim; \_.:.-5:\3~ .-\ _,.~\. \~.\.\. ww . . w \-. .\.\_ x. .um \_l folding the exposed part coated with a conductive adhesive to provide a surface In some embodiments, step (b) of the method may comprise abutted against the electrode roll assembly, the conductive adhesive comprising a polymeric binder and conductive particles dispersed therein, said folded exposed part being optionally secured in the folded position by the conductive adhesive; bonding the first current collecting plate to the exposed part of the first electrode with a conductive adhesive, thereby providing electrical conductivity between the exposed part of the first electrode and the first current collecting plate.

In some embodiments, prior to step (b), the method comprises the further step of *S \ ~ applying a roughening process to the first current collecting plate» 4 in order to increase the surface roughness of a surface of the first current collecting plateg; \ ¿>_of the first electrode. be bonded to the exposed part In some embodiments, the exposed part extending from the end of the electrode roll assembly is not fully abutted against the electrode roll assembly, and wherein step (b) comprises applying conductive adhesive to the first current collector, and pressing the first current collector onto the exposed part of the first electrode, simultaneously folding and abutting the exposed part of the first electrode against the rolled electrode assembly ensuring contact adhesion and electrical conductivity between the first current collector and the exposed part of the first electrode. _ _~ :___ .__ .to I . ___. _.......,._t_. ~\« V.. »v ~ .~\~~ \. s.. .in \_.\.«..~~\ - In some embodiments, the step of applying the first conductive adhesive component to the exposed part» of the first electrode comprises applying the first conductive adhesive to cover a portion of the exposed part = substantially congruent with the shape of the first current collecting plate»¿§§§ïj.=_.

In some embodiments, the step of abutting the first current collecting plate gfjgﬁgšggagainst the exposed part gmcomprises radially and concentrically aligning the first current collecting plate registration with the first conductive adhesive component applied to the exposed pa rtggg' In some embodiments, the first conductive adhesive component comprises the *\ \ ';¿¿>_and a crosslinkable polymerggjlgš conductive particles and the second conductive Q É XZJ. ' adhesive component comprises an activatorgi In some embodiments, the method comprises the further steps of: placing the electrode roll assembly in a casing, the casing comprising a terminal part; and welding the terminal part to the first current collecting plate, wherein the welding generates heat that causes at least partial curing of the conductive adhesive.

In some embodiments, the electrode roll assemblym=f§§§_š_ comprises a second electrode wound about the central axis, the second electrode comprising an exposed part \ gwextending from a second end of the electrode roll assemblygfj§j§_; and the method further comprises: providing a second current collecting plate; and using conductive adhesive» to join the second current collecting plate to the exposed part 'jgwof the second electrode, thereby providing electrical conductivity between the exposed part ymof the second electrode and the second current collecting plate.

While the disclosure is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example and will be described in detail. It should be understood, however, that other embodiments, beyond the particular embodiments described, are possible as well. All modifications, equivalents, and alternative embodiments falling within the spirit and scope of the appended claims are covered as well.

The above discussion is not intended to represent every example embodiment or every implementation within the scope of the current or future Claim sets. The figures and Detailed Description that follow also exemplify various example embodiments. Various example embodiments may be more completely understood in consideration of the following Detailed Description.

BRIEF DESCRIPTION OF THE DRAWINGS One or more embodiments will now be described by way of example only with reference to the accompanying drawings, in which: Figure 1 schematically illustrates a secondary cell ::::\:I:.;:íï::~:;.;~.ít to? 1-22? .\._..\. _ a., , ;: .ct , ;,\._._ , ;.;. , . .Ncc \.\._\.~\.~\.I\ .~~ .~.\., ~..\- ..~.\..\.~.~, Figure 2 schematically illustrates an isometric view of a partially wound electrode roll assembly; Figure 3 schematically illustrates a close-up view of the secondary cell of Figure 1, particularly the construction of a terminal; Figure 4 schematically illustrates a close-up view of the connection shown in Figure 3, particularly a joint between a current collecting plate and the electrode roll assembly; Figure 5 schematically illustrates a method ofjoining the current collecting plate to the electrode roll assembly; Figure 6 schematically illustrates a tab-less secondary cell----«;=;~;=_, . cwg _ __:;.. _ Mg. __.\~: :.;.>_.\ 4:;..._\ _\__.,.\_.\_._;_ _26 LLM ga .....,.>\:_ W. and \ v -^\»*\*.. .f~\\. \.'\ yunx.. \\.~.~_. \.\\. k-'wmfm \.'n \.~\\.- x.. . \./\~-.. .^\~, Figure 7 schematically represents a method of manufacturing a secondary cell according to an embodiment of the ssee<=_>\.=§: .ßaspect of the invention. DETAILED DESCRIPTION When the following directions like "up", "down", "left" and "right" are used they always refer to the respective figure referenced.

Embodiments of the present disclosure will now be described more fully hereinafter, with reference to the figures. The same reference numbers are used throughout the figures. The invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those persons skilled in the art.

Figure 1 illustrates a secondary cell 1 (hereinafter also referred to as the cell 1).

Herein, the terms "inner' and "outer' are used with reference to the centre of the cell The cell 1 comprises a substantially cylindrical casing, also referred to as a can 2, and a cylinder-shaped electrode roll assembly 5, which may also be considered as a jellyroll or Swiss roll, arranged inside the can 2. In this embodiment of the invention, the can 2 is also filled with a liquid electrolyte (not shown).

Figure 2 shows the electrode roll assembly 5 of Figure 1 in a partially rolled state. The electrode roll assembly 5 comprises first and second conductive sheets 4, 4', each sheet coated with a respective electrode coating 41, 41'.

The electrode coating 41 on the first conductive sheet 4 may constitute an active part of the positive electrode/cathode of the cell 1. In which case, the electrode coating 41' of the second conductive sheet 4' constitutes an active part of the negative electrode/anode of the cell 1. Alternatively, the anode and cathode may be arranged on the first and second conductive sheet respectively.

The materials of the conductive sheets 4, 4' and the electrode coatings thereon are known in the art. Suitable materials for the conductive sheets 4, 4' include copper (often used for the anode) and aluminium (often used for the cathode).

Electrode coatings are typically may be formed from electrode coating material comprising an active component, a binder (which is usually a polymer) and optionally a conductive component, typically at a weight ratio of about 98:1:1. The active component typically differs for the anode and cathode.

For the cathode, the active component is typically a material containing lithium which can be easily released, such as a lithium transition metal complex, with lithium nickel manganese cobalt oxides (NMC) typically being used.

For the anode, the active component is typically a material capable of taking up lithium, such as graphite.

The two conductive sheets 4, 4' are arranged with a separator positioned therebetween. In particular, the electrode roll assembly 5 comprises first and second separator sheets 6, 6'. The first separator sheet 6 is positioned directly between the two conductive sheets 4, 4' and the second separator sheet 6' is positioned to cover an outer surface of the second conductive sheet 4' so that it separates the outer surface of the second conductive sheet 4' from the inner surface of the first conductive sheet 4 of an adjacent layer of wound sheets.

In other embodiments of the invention, a solid electrolyte may be used. In such embodiments, each separator sheet 6, 6' may be replaced by a sheet of solid electrolyte. Alternatively, solid electrolyte may be applied as a coating to the positive electrode coatings, the negative electrode coatings or the electrode coatings of both electrodes. It should be noted that although aspects of the invention are generally described with respect to secondary cells comprising liquid electrolyte, the various features are equally applicable, mutatis mutandis, to secondary cells comprising solid electrolyte. Also, other designs of known secondary cells are readily combinable with the aspects of the invention, for example other designs of the terminals, can or current collecting plate.

Referring back to Figure 2, the conductive sheets 4, 4' (and the separator sheets 6, 6') are wound into a cylindrical shape to form the electrode roll assembly 5. In er _. "qi . ._=;.. _ .t;_,_. _, :t ma, g i 'C m ' I the electrode roll assembly 5 may be wound to have a non-circular cross-section, such as an oval- or obround-shaped cross-section.

The first conductive sheet 4 comprises an exposed part 43 free from electrode coating 41 along a longitudinal edge 4a. Similarly, the second conductive sheet 4' also comprises an exposed part 43' along a longitudinal edge 4a'. However, the first and second conductive sheets 4, 4' are arranged in the electrode roll assembly 5 so that the exposed part 43 of the first conductive sheet 4 is positioned at an opposite end of the electrode roll assembly 5 to the exposed part 43' of the second conductive sheet 4'. The exposed parts 43, 43' provide for physical and electrical connection between each electrode and a respective terminal.

Notches 45 are cut (for example, by laser), or otherwise formed, in each of the exposed parts 43, 43'. More specifically, notches 45 are formed in the longitudinal edge 4a of each conductive sheet 4, 4' which is free from coating. Due to the notches 45, f|aps 44 are formed in the exposed parts 43, 43'. Hence, each notch 45 separates two consecutive f|aps 44. The f|aps 44 can be bent inwards towards a winding axis 40 of the electrode roll assembly 5 after the different stacked layers of the cell 1 have been rolled up. The bent f|aps 44 form a contact surface 12 that enables improved electrical and physical connection to another component.

The above-described notching process is not always necessary. x "the exposed parts 43, 43' may be pressed or crushed to form a contact surface. The direction of press or crush may be coaxial with and towards the centre of the electrode roll assembly 5, for example.

Referring again to Figure 1, the cell 1 further comprises a current collecting plate 7 In this that is arranged adjacent to one end of the electrode roll assembly 5. ' " " the current collecting plate 7 isjoined to the exposed part 43 of the first conductive sheet 4 of the electrode roll assembly 5, specifically the contact surface 12 (shown in Figure 2). In other words, the current collecting plateis joined to the exposed part 43 of the positive electrode.

The cell 1 has a positive terminal (+) and a negative terminal (-). The can 2 comprises a central terminal through-hole 11 for a terminal part 3 forming part of the positive terminal. The terminal part 3 is in electrical contact with the current collecting plate 7 which is, in turn, connected to the positive electrode, as described above. The negative terminal is electrically connected to negative electrode via any suitable means (not shown). The cell 1 typically includes a plurality of other components such as vents, connectors and insulating parts etc. There are many ways to design these parts known to a person skilled in the art and they will not be described herein.

The connection of the current collecting plate 7 to the exposed part 43 is more clearly shown in Figures 3 and The current collecting plate 7 is joined to the contact surface 12 of the exposed part 43 by a conductive adhesive 20. Figure 4 also shows more clearly how the contact surface 12 is formed from the folded f|aps 44 of the exposed part 43. Although the cross-sectional drawing appears to show multiple separate exposed parts 43, it is to be understood that this is in fact one continuous component by virtue of the fact that the conductive sheet 4 is wound about the winding axis, as shown in Figure The conductive adhesive 20 comprises a polymeric binder 22 and conductive particles 24 dispersed therein. The conductive adhesive is arranged to ensure electrical connection between the contact surface 12 and the current collecting disc 7. Typically, this is achieved via direct physical contact between the contact surface 12, the conductive particles 24 and the current collecting disc 7 which provides for electrical conductivity.

The conductive particles 24 may be any suitable conductive material, including conductive carbon such as graphite or a conductive metal such as silver, gold, nickel, or copper.

Preferred conductive particles are selected from graphite, copper or silver.

In some embodiments of the invention, the conductive particles are silver particles to benefit from the high electrical conductivity of silver and, thereby, reduce resistance in the cell.

The conductive particles are typically from 1 to 50 um, usually from 1 to 25 um.

By "particle size", it is meant tree average primary' gaarti-:Ee size (rnean particle diameter, rise) determined by means of laser dâffracrtion. Laser :íiffracïíian measurements car: be carried aut making use of a particie size analyzer, 'for example, a Eviastersizer Eäüüi) 'fram iriaiverr: ïnstrumerrts.

The polymeric binder 22 may be non-porous and may comprise any suitable type of adhesive for joining the current collecting plate 7 to the contact surface 12. For example, in some embodiments of the invention, the polymeric binder mase-compriseg; *e-xar-a reactive adhesive.

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L". .i "W ~.-i~..-.~l _ .-.- .i - -..:.-- x'-.-. ...-.- . "x - v.. =§~ _* L. i-kf. -ﬂw-ﬁf-iwf. . _ x~.~ _x~~.~. i . _. _..-.-._..i.~ _°_.~ ..~.. i.. . x.~..._«. -._..~.. .~..~x_~ x.~:.-.._.~w_.. . ._x.~ ._.i_.. ..f..i. e... ..._ ___. .__ -.._ .x . -. i_. x ._51 -.. w .« ~i.-ix"-'~.~« i~.~...-i i-iw-.vx :vi _-.- . i--~~i~~"~ wøiïi-Ä» w-i- V» I f".- « -x- - i.«..-i*-=i i \ ii..i ...~ .i .ii.._. i. .ix \i.._...-....../x.. x i~.._.. ~.. ~ ....~../.. ...ii . .i ......... ~ ii i _ .i ~ vi i v .i-x i 'i w w i i .. ~ -_ hi ~ - x .x .xi- vi i x '- «i~i . .«i-w-x~ xi. i . x.ii .i . lix ._ x .ii.__. i. . i. y ~ x...- x xi. x. ii ii.._..w i . . .x.~../..ix~ , .i..i \.....:. ..\:._:;.\ __. _. .. _. . _ .~".i\.ii .i.\ xfïi.. iiix A multi-part or multi-component adhesive cures once two or more components are mixed together, allowing them to chemically react. This reaction causes polymers to cross-link, usually into acrylates, urethanes or epoxies.

Exemplary combinations of multi-component adhesives include: polyester resin and polyurethane resin; polyols and polyurethane resin; and acrylic polymer and polyurethane resin.

Typically, a multi-part adhesive will comprise a polymeric component in a first part, and an activator in a second part. The activator will typically promote a reaction in the polymer, such as crosslinking of the polymer chains. The activator may require astimulus such as heat. Activators that require actinic radiation such as UV to promote crosslinking are typically less preferred, as it is not usually possible to expose the conductive composition to the actinic radiation given that it is disposed between the current collector and exposed part of the electrodes.

A multi-part adhesive may cure rapidly on mixing, or may require heat activation (i.e. a heat-curing adhesive).

In some embodiments, the multi-part adhesive contains a first component applied to the current collector, and a second component applied to the contact surface, such that on contacting the current collector and contact surface the first and second components mix to form the multi-part adhesive.

In some embodiments, the multi-part adhesive is heat activated, and curing is achieved by heating the multi-part adhesive when the current collector is in contact with the contact surface. Such heat may be provided by the welding step when the current collector is welded to the terminal of the cell.

Although such a~.~'=.« polymeric binder would require the provision of heat, which is an aspect of known welding processes that the invention is aiming to avoid, the heat required for adhesive curing may be significantly lower than the heat generated by welding. This factor is particularly relevant with respect to heat exhibited in close proximity to the electrode roll assembly, where resulting damage to the cell is most likely.

Irrespective of the type of polymeric binder 22 that is used, the use of a conductive adhesive 20 avoids issues associated with welding the current collecting plate 7 to the electrode roll assembly 5. For example, whereas welding is carried out very quickly and therefore provides little margin for error, the use of conductive adhesive allows for adjustments or corrections to be made in the positioning of the current collecting plate with respect to the electrode roll assembly to ensure a good connection between the two components. Also, as the use of a conductive adhesive requires no provision or generation of heat or, if a heat-curing adhesive is used, significantly less heat than welding, potential damage to the exposed part and/or proximal portions of the electrode roll assembly can be avoided and the risk of a short circuit reduced.

When the conductive adhesive or a component thereof is applied to the exposed part of the electrode roll assembly prior to contact with the current collector, the strengthand rigidity of the exposed part is increased, making it easier to manipulate and position in preparation for contact with the current collector. The increased strength and rigidity of the exposed part reduces the risk of damage during the folding process, as well as increases the accuracy of positioning in preparation for contact with the current collector.

In general, these advantages are achieved through the use of a conductive adhesive applied to the exposed part of the electrode. However, optionally the conductive adhesive may be applied to the exposed part specifically to facilitate folding of the exposed part during manufacture.

Thus, in some embodiments, step (a) of the method may comprise: providing an electrode roll assembly and a first current collecting plate, the electrode roll assembly comprising a first electrode wound about a central axis, the first electrode comprising an exposed part extending from a first end of the electrode roll assembly, at least part of said exposed part having a conductive adhesive coated thereon.

The at least part of the exposed part coated with a conductive adhesive has increased rigidity and increased tensile strength compared to the uncoated portions, thereby facilitating the further manufacturing steps such as preparing the exposed part for bonding to the current collector (e.g. by folding and/or flattening the exposed part).

The conductive adhesive may be applied to the exposed part prior to winding the electrode assembly. In such embodiments, the conductive adhesive is applied at an earlier stage of the manufacturing process, and typically has low or no tackiness when rolling. The conductive adhesive may for instance be a hot melt adhesive which is applied and allowed to cool.

In some embodiments, step (b) of the method may comprise: folding the exposed part at least partially coated with a conductive adhesive to provide a surface abutted against the electrode roll assembly, said folded exposed part being optionally secured in the folded position by the conductive adhesive; bonding the first current collecting plate to the exposed part of the first electrode with conductive adhesive, thereby providing electrical conductivity between the exposed part of the first electrode and the first current collecting plate.The use of a multi-part adhesive may be particularly beneficial as it may assist with the manufacture of the cell 1. In such embodiments of the invention, the curing of the conductive adhesive 20 may be triggered without needing to wait for evaporation of a solvent and without needing to introduce heat, thereby accelerating and/or simplifying the manufacturing process.

For example, as shown in Figure 5, a first conductive adhesive component maybe applied to the exposed part 4, specifically the contact surface. The first conductive adhesive component may comprise paste with a crosslinkable polymer 26 in addition to the conductive particles 24. Meanwhile, a second conductive adhesive component may be applied to the current collecting plate 7, the second conductive adhesive component comprising an activator 28. Applying the polymeric component to the exposed part 4 is preferred as it advantageously increases the strength and rigidity of this component, facilitating the further manufacturing steps.

With the two conductive adhesive components applied, the current collecting plate 7 may be abutted against the exposed part 43 so that the activator 28 contacts and mixes with the crosslinkable polymer 26, initiating curing of the conductive adhesive 20. The abutment of the current collecting plate 7 against the exposed part 43 also causes the conductive particles 24 to be compressed together in between the opposing surfaces of the collecting plate 7 and exposed part 43, thereby causing the compressed configuration represented in Figure 4 that allows for electrical conductivity.

To assist the effectiveness of the conductive ad hesive 20 in robustly joining the current collecting plate 7 to the exposed part 43, the current collecting plate 7 may comprise a roughened surface 14. That is, a surface to which a roughening process has been applied in order to increase the surface roughness of the current collecting plate 7. The increased surface roughness of the roughened surface 14 provides a texture into which the polymeric binder 22 may flow while in its mobile (or uncured) state. Then, once the polymeric binder has been processed (e.g. cured) to a solid state, it essentially grips the texture of the roughened surface 14. It is to be understood that a roughened surface 14 may be used beneficially with any conductive adhesive 20 and is not uniquely applicable to or beneficial for multi-part adhesives.

Advantageously, the conductive adhesive (or conductive adhesive component) is applied to the electrode (i.e. the exposed part) to cover a portion of the first electrode substantially congruent with the shape of the current collecting plate. The currentcollecting plate is then radially aligned in registration with the conductive adhesive component on the electrode when abutting the current collecting plate to the electrode.

In some embodiments, the use of a conductive adhesive can lead to manufacturing advantages. For instance, the exposed part of the first electrode typically needs to be folded and pressed to form a suitable surface for adhesion to the current collector. This folding/preparation step may be expedited or even omitted by using an adhesive. For instance, a conductive adhesive may be applied to the current collector, which is then pressed onto the exposed part of the first electrode, simultaneously folding and abutting the exposed part against the rolled stack and ensuring contact adhesion and electrical conductivity with the current collector. In such processes, the exposed part of the first electrode is not fully abutted against the rolled stack prior to contact with the current collector.

Particularly suitable adhesives for such methods include hot melt adhesives.

In Figure 6, a cell 101 is shown which is similar to the cell 1 shown in Figure 1 except that the connection of the negative electrode/anode to the negative terminal is shown. The construction of this connection resembles that of the connection between the positive electrode and the positive terminal.

In particular, the cell 101 comprises a first current collecting plate 7 (equivalent to the current collecting plate 7 shown in Figure 1) and a second current collecting plate 107 arranged adjacent to the electrode roll assembly 5 but at the opposite end to the first current collecting plate 7. The exposed part 43' of the negative electrode extends from the other sheets in the electrode roll assembly 5 and is joined to the second current collecting plate 107. The second current collecting plate 107 may be attached by way of conductive adhesive 20, as described above in relation to the current collecting plate 7 shown in Figures 1, 3, 4 and The can 2 further comprises a terminal part 103 forming the negative terminal. The terminal part 3 is in electrical contact with the current collecting plate 107. The cell 101 may also include a plurality of other components such as vents, connectors and insulating parts. There are many ways to design these parts known to a person skilled in the art and they will not be described herein.

The cell 1 of Figure 1 and the cell 101 of Figure 6 may be manufactured by any suitable method but may particularly be manufactured by a method according to an embodiment of the second aspect of the invention.

It is to be understood that either one, or both, of the cell terminals may have a construction similar to that described above and that methods of manufacturing an electrode according to embodiments of the invention may improve the performance, safety and/or reliability of such cells by virtue of one or more high edges being removed.

Figure 7 shows a method 200 of manufacturing the cell 101 of Figure 6. The method 200 comprises initial steps of providing the electrode roll assembly 5 (step 202); providing a first current collecting plate 7 (step 204); and using conductive adhesive to join the first current collecting plate 7 to the electrode roll assembly 5 (step 206).

As described above, the electrode roll assembly 5 comprises a first electrode wound about a central axis, the first electrode comprising an exposed part 43 extending from a first end of the electrode roll assembly 5. In this embodiment of the invention, the first electrode is the positive electrode/cathode and the first current collecting plateis the positive current collecting plate Step 206 therefore comprises using conductive adhesive 20 to join the positive current collecting plate 7 to the exposed part 43 of the positive electrode. The conductive adhesive 20 comprises an polymeric binder 22 and conductive particles 24 dispersed therein and provides electrical conductivity between the exposed part 43 of the positive electrode and the positive current collecting plate Subsequently, the method 200 may comprise further steps of providing the can 2 (step 208); placing the electrode roll assembly 5 (with the joined positive current collecting plate 7) into the can 2 (step 210); providing the terminal part 3 for the positive terminal (step 212); and welding the terminal part 3 to the positive current collecting plate 7 (step 214). a heat-curing adhesive is used to form the conductive adhesive 20, the heat generated during welding of the terminal part 3 to the positive current collecting plate 7 may cause the conductive adhesive to cure, at least sufficiently for further manufacturing steps to take place without risk of the current connecting plate 7 becoming displaced from the electrode roll assembly\-,.\\ . mi., . » <-.«- . «'«-\«~, , 1A _-. ,q.;. , 1,. ~ ~ ~ gr. . ._ _: *.~y'*.í:^:i^: a drying adhesive is used, it may be necessary to store the electrode roll assembly for a period of time, to allow drying of the adhesive to occur, before other manufacturing steps are resumed. For example, the method may include an additional step, subsequent to step 206, of storing the electrode roll assembly for a predetermined period of time such as 2 hours, 4 hours or 24 hours.

If a multi-part adhesive is used, the curing reaction may occur in a matter of minutes, or even just seconds and it may be that no storage or heating is required.

The amount of conductive particles and polymeric binder present in the conductive adhesive will vary depending on the type of polymeric binder that is used. Typically, the amount of polymeric binder is relatively low, to ensure the conductivity of the adhesive is high. Additionally, the adhesive force required is relatively low, as the current collector and contact surface undergo relatively low amounts of sheer force when held in place in the sealed cell.

Exemplary conductive adhesives contain from 70 to 98 wt% conductive particles, and from 2 to 30 wt% polymeric binder.

When a drying adhesive is used, the formulation used to form the conductive adhesive additionally contains solvent which is removed as the adhesive dries.

The method 200 may comprise further steps of providing a second/negative current collecting plate 107 (step 216); using conductive adhesive 20 to join the second/negative current collecting plate 107 to the electrode roll assembly 5 (step 218); providing the terminal part 103 for the negative terminal (step 220); and welding the terminal part 103 to the second/negative current collecting plate 107 (step 222).

Steps 216 to 222 may be carried out similarly to the corresponding steps related to the positive terminal (i.e., steps 204, 206, 212 and 214).

It is to be understood that there may be additional manufacturing steps that precede the steps outlined above, such as preparing the electrode roll assembly; preparing the current collecting plates; and preparing, cleaning and testing the can. Similarly, there may be manufacturing steps added in between steps referred to above, such as the storage step described earlier for allowing the conductive adhesive to dry. There mayalso be further steps that follow step 222. For example, additional steps may include connecting additional components (such as vents, connectors and insulating parts) to the cell 1 and testing the cell (e.g., H-Pt testing, X-Ray testing and helium leak testing). However, such steps are known to persons skilled in the art and are not the focus of this disclosure, hence they are not described in detail in this disclosure.

Although specific terms may be employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation. Therefore, persons skilled in the art would recognize numerous va riations to the described embodiments that would still fall within the scope of the appended claims. As used herein, the terms "comprise/comprises" or "include/includes" do not exclude the presence of other elements or steps. Furthermore, although individual features may be included in different claims (or embodiments), these may possibly advantageously be combined, and the inclusion of different claims (or embodiments) does not imply that a certain combination of features is not feasible and/or advantageous. In addition, singular references do not exclude a plurality. Finally, reference numerals in the claims are provided merely as a clarifying example and should not be construed as limiting the scope of the claims in any way. 18

Claims

1. A method of manufacturing a secondary cell, the method comprising the steps of: (a) providing an electrode roll assembly>¿§¿§§¿j¿ and a first current collecting plateM§§§~É_š_, \ the electrode roll assemblymijš: comprising a first electrode wound about a central axis, the first electrode comprising an exposed extending from a first end of the electrode roll assembly comprising a conductive sheet ífïšlggnot coated with active material; and (b) bonding the first current collecting platewåjšgﬁ) to the exposed part = of the first electrode with a conductive adhesive, the conductive adhesive “comprising a polymeric bindergi and conductive particlesi dispersed therein, thereby providing electrical conductivity between the exposed part» of the first electrode and the first current collecting platewgfg§ïgﬁ_ï, wherein step (a) comprises bending, pressing or crushing the exposed part towards a centre of the electrode roll assembly3f>§§_š_ to form a contact surfacemi and wherein the polymeric bindergíg comprises a multi-part adhesive, and step (b) comprises: applying a first conductive adhesive component to the contact surfacei and applying a second conductive adhesive component to the first current collecting plate the first and second conductive adhesive components being unreactive when separate and configured to form a self-curing, multi-part adhesive upon mixing; and abutting the first current collecting platewjloišïš against the contact surface,»5;@;¿>;§_š_ until the multi-part adhesive is sufficiently cured to hold the first current collecting \ ~ plategfg§§~ﬁjg_ against the exposed partw;

2. The method of claim 1, wherein, prior to step (b), the method comprises the further step of applying a roughening process to the first current collecting plate>§>§§ïf_s_ in order to increase the surface roughness of a surface of the first current collecting plate

3. The method of claim 1 or claim 2, wherein the step of applying the first conductive adhesive component to the exposed part E) of the first electrode comprises applying the first conductive adhesivee- to cover a portion of the exposed _)\ ~~ ii substantially congruent with the shape of the first current collecting plate

4. The method of claim 3, wherein the step of abutting the first current collecting plategígšgﬁï against the exposed part g; comprises radially and concentrically aligning \'\ the first current collecting plate in registration with the first conductive adhesive component applied to the to the exposed parti

5. The method of any preceding claim, wherein the first conductive adhesive \ and a crosslinkable polymerg; component comprises the conductive particles» and the second conductive adhesive component comprises an activatorgfggšgåïgï.

6. The method of any preceding claims, wherein the electrode roll assemblygígíšgï comprises a second electrode wound about the central axis, the second electrode comprising an exposed partgfig- 1 extending from a second end of the electrode roll assembly,»§§§_š_; the method further comprising: providing a second current collecting plate; and \ _.\\ using conductive adhesive» g to join the second current collecting plate to the exposed of the second electrode, thereby providing electrical conductivity between the exposed partmåg- 1 of the second electrode and the second current collecting plate.